1. Field of the Invention
The present invention relates generally to the field of high speed data transfer, and more specifically to mapping cell or packets in accordance with the SONET/SDH architecture.
2. Description of the Related Art
Data transmission over fiber optics networks may conform to the SONET and/or SDH standards. Data may be processed using a mapper, where the mapper reads and processes packets from system queues and adds idle packets or cells when the queues are empty. The mapper conforms to SONET/SDH requirements as well as the SPI-4 Phase 2 requirements. SONET and SDH are a set of related standards for synchronous data transmission over fiber optic networks. SONET is short for Synchronous Optical NETwork and SDH is an acronym for Synchronous Digital Hierarchy. SONET is the United States version of the standard published by the American National Standards Institute (ANSI). SDH is the international version of the standard published by the International Telecommunications Union (ITU). As used herein, the SONET/SDH and SPI-4 Phase 2 concepts are more fully detailed in various documents, including but not limited to the discussion of SPI-4, Phase 2, in the Optical Internetworking Forum (OIF Document) OIF-SPI4-02.1 and the discussion of concatenated payloads in ITU-T G.707 2000, T1.105-2001 (draft), and T1.105.02-1995.
SONET/SDH may employ payloads called virtually concatenated payloads. Virtual concatenation, as differentiated from contiguous concatenation, partitions the payload into virtual containers that may be provided with a single index and transmitted at one time, but may be received and processed at different times. Virtual concatenation allows for data delays through the network where the receiving entity can reassemble the payload irrespective of the time the payload components are received.
When using a mapper conforming to the aforementioned SONET/SDH and SPI-4 Phase 2 requirements, the bandwidth of each constituent signal in the SONET/SDH frame may change dynamically, or on the fly, during packet reading and processing. Data requests from the SONET/SDH frame builder blocks to the mappers do not follow a constant or uniform sequence, and may be received out of order or in a random order. For example, data in virtually concatenated payloads may be received at anytime and are based on the amount of delay incurred while traveling through the network. These blocks may be unavailable on an as needed, cycle by cycle basis.
In accordance with the framing and mapping process, it may be beneficial to have data available from different blocks and packets, such as from different virtual concatenation groups, on a cycle by cycle basis.